Summary/Abstract: Ubiquitous chemical exposures during pregnancy have escalated to the level where phthalates and other endocrine disrupting chemicals (EDCs) may be reducing fertility in current and in future generations. Several human studies have shown relationships between higher adult phthalate exposure and reduced fertility in men and women. Extensive evidence from animal studies indicate that phthalates can cause defects in the developing reproductive system (ovaries, testes, genitalia) of the fetus. However, attempts to understand if the human fetus is similarly vulnerable have not been successful. This may be due to the omission of the human placenta in these studies. The placenta plays an important, species-specific and sex- specific role in responding to maternal phthalate exposures and directing the sexual differentiation of the fetus. The proposed project will evaluate the role that the human placenta may play in mediating the effects of phthalates on fetal reproductive system development in early human pregnancy (i.e. fetal origins of infertility). Aim 1 will compare phthalate concentrations in matched placental tissue/maternal urine to determine if standard biomarkers of phthalate exposure in maternal urine are representative of placental phthalate concentrations, more proximal to the fetus. The placental tissue and maternal urinary metabolomes (an unbiased analysis of 10,000 endogenous metabolites) will be correlated with phthalate levels in order to identify novel biomarkers of phthalate exposure, metabolism, and sex-specific fetal effects. Aim 2 will use human primary tissue culture models to re-establish communication between the placenta and the fetal gonad ex vivo. Placental 3D cultures will be dosed with phthalate concentrations equivalent to those measured in placental tissue. The secreted placental proteins from these experiments will then be placed on 3D fetal gonads (+/- phthalates, +/- placental proteins), matched by sex and gestational age. We will determine if and how fetal steroidogenesis is altered by phthalates exposure, via the placenta. Aim 3 will translate these findings to 500 pregnancies in two existing longitudinal birth cohorts. First, we will measure a panel of placenta-, phthalate-, and sex- specific biomarkers in the first trimester. We will calculate their associations with neonatal anogenital distance at birth (a marker of future fertility), and to birth size and neonatal adiposity (markers of general placental function and also relevant to the future health of the child). Finally, statistical techniques will be applied to estimate the degree to which the phthalate associations with reproductive system development are mediated by phthalate effects on the early placenta. Greater knowledge of early pregnancy exposures, effects, and specific ways to assess placental-fetal well-being open the possibility to move prenatal screening earlier, incorporate assessment of environmentally-induced risks and potentially reduce population trends in male and female infertility.